The present invention relates to a bidirectional (two-way) optical communication device and a bidirectional optical communication apparatus which can carry out bidirectional optical communication simultaneously by using a single optical fiber.
With respect to conventional bidirectional optical communication devices used for bidirectional optical communication links (bidirectional optical communication apparatuses), Japanese Laid-Open Patent Application No. 279627/1988 (Tokukaishou 63-279627) discloses such a device (first prior art). As illustrated in FIG. 9, this bidirectional optical communication device is provided with a first optical communication module 32 and a second optical communication module 36. The first optical communication module 32 and the second optical communication module 36 are respectively connected to one end and the other end of a single polarization-maintaining optical fiber 31.
Moreover, the first optical communication module 32 is provided with a first wave guide polarizing beam splitter 33, a first semiconductor laser 34 and a first photo-detector 35. The second optical communication module 36 is provided with a second wave guide polarizing beam splitter 37, a second semiconductor laser 38 and a second photo-detector 39. Here, the wave guide polarizing beam splitters 33 and 37, which are made from a birefringence substance such as LiNbO3, function to transmit TE (Transverse Electric) mode light projected from the semiconductor lasers 34 and 38 so as to project TM (Transverse Magnetic) mode light on the lower faces of substrates 40 and 40xe2x80x2.
The TE mode light, projected from the first semiconductor laser 34 of the first optical communication module 32, is transmitted through the first wave guide polarizing beam splitter 33, coupled to the polarization-maintaining optical fiber 31, transferred through the polarization-maintaining optical fiber 31 while maintaining its plane of polarization, emitted from the other end of the polarization-maintaining optical fiber 31 and guided to the second optical communication module 36.
As illustrated in FIG. 10, the first optical communication module 32 and the second optical communication module 36, connected to the polarization-maintaining optical fiber 31, are installed so that planes of polarization of the respective output lights are aligned orthogonal to each other. For this reason, the output light of the first optical communication module 32 forms TM mode light in the second optical communication module 36, with the result that it is not transmitted through the second wave guide polarizing beam splitter 37, and detected by the second photo-detector 39 installed on the lower surface of the substrate 40xe2x80x2. In the same manner, the output light from the second optical communication module 36 is also detected by the first photo-detector 35 in the first optical communication module 32.
Moreover, with respect to another conventional bidirectional optical communication link, Japanese Laid-Open Patent Application No. 262276/1996 (Tokukaihei 8-262276) discloses such a link (second prior art). As illustrated in FIG. 11, this bidirectional optical communication link is constituted by a light-emitting element 41 and a light-receiving element 42, two lenses 45 and 46, a wavelength filter 43 that transmits light having the first wavelength xcex1 and reflects light having the second wavelength xcex2, and an optical fiber 44 whose light inputting and outputting end face 44a is diagonally polished. Here, the light-emitting element 41, the light-receiving element 42, two lenses 45 and 46 and the waveform filter 43 constitute a bidirectional optical communication device.
Light having the first wavelength xcex1 released from the light emitting element 41 is converged by the first lens 45, and coupled to the optical fiber 44 through the wavelength filter 43. Light having the second wavelength xcex2, which is an inputted light from the optical fiber 44, is reflected by the wavelength filter 43, converged by the second lens 46 and coupled to the light-receiving element 42.
In the case when the end face 44a is placed so as to be orthogonal to the inputted light, a portion of the light having the first wavelength xcex1 is reflected by the end face 44a, and the reflected light is again reflected by the wavelength filter 43 and directed to the light-receiving element 42, with the result that cross talk tends to occur. However, in this second prior art, since the end face 44a is tilted, the reflected light from the end face 44a of the optical fiber 44 is not allowed to enter the second lens 46, thereby reducing cross talk.
Here, the first and second prior arts have the following problems: In the first prior art, expensive members, such as the polarization-maintaining optical fiber 31 and the wave guide polarizing beam splitters 33 and 37, are required, resulting in high costs, and since the polarization-maintaining optical fiber 31 is a single-mode optical fiber with a small core diameter of several xcexcm, with the result that time-consuming tasks are required in positioning the respective optical communication modules 32 and 36 and the polarization-maintaining optical fiber 31 to each other.
In the second prior art, the light-emitting elements 41 such as semiconductors, etc., having mutually different generating waveforms and the bidirectional optical communication devices provided with the wavelength filters 43 having mutually different transmitting wavelengths have to be installed at both of the ends of the optical fiber 44, and the characteristics of the respective bidirectional optical communication devices have to be changed. This makes the construction of bidirectional optical communication links complex, and results in difficulty in reducing the costs of the bidirectional optical communication device and the bidirectional optical communication link using those parts.
In order to address the above-mentioned problems, the objective of the present invention is to provide a bidirectional optical communication device and a bidirectional optical communication link using the device in which the bidirectional optical communication device and an optical fiber are easily positioned at low costs.
In order to solve the above-mentioned problems, a bidirectional optical communication device in accordance with the present invention is provided with: a light-emitting element for generating signal light in accordance with a data signal, a light-receiving element for receiving the signal light and for generating a data signal in accordance with the signal light, a transmitting light wave guide for projecting transmission light that is the signal light from the light-emitting element to an optical fiber outside, a received light wave guide for guiding received light that is signal light from the optical fiber outside, and a positioning means for positioning the transmitting light wave guide, the received light wave guide and the optical fiber so as to optically connect with one another, wherein: the transmitting light wave guide and the received light wave guide are mutually optically separated from each other, and the light axis of the transmission light is set so as to tilt with respect to the normal to the end face of the optical fiber.
With the above-mentioned arrangement, in the case when the above-mentioned arrangements are connected to both of the ends of an optical fiber so as to form a bidirectional optical communication apparatus, signal light from the light-emitting element is coupled to the optical fiber through the transmitting light wave guide, and transferred to one end to the other end of the optical fiber, while signal light from the optical fiber is sent through the received light wave guide, and received by the light-receiving element at which the corresponding data is generated.
Thus, the above-mentioned arrangement makes it possible to transfer transmitting light and received light bidirectionally using a single optical fiber for transmitting signal light, thereby allowing bidirectional communication.
Moreover, in the above-mentioned arrangement, the transmitting light wave guide and the received light wave guide are mutually optically separated, and the light axis of transmitting light is set by the positioning means so as to tilt with respect to the normal to the end face of the optical fiber; thus, it is possible to avoid the transmitting light from the transmitting light wave guide from entering the received light wave guide.
Therefore, the above-mentioned arrangement eliminates the need for expensive optical elements conventionally used, such as polarizing beam splitters and wavelength filters, separates the transmitting light and received light from each other, and carries out bidirectional optical communication simultaneously at low costs by using a single optical fiber.
In order to solve the above-mentioned problems, a bidirectional optical communication apparatus in accordance with the present invention is provided with: an optical fiber for transmitting signal light in a multi mode, and bidirectional optical communication devices that are respectively coupled to both of the end faces of the optical fiber, said bidirectional optical communication device being provided with a light-emitting element for generating signal light in accordance with a data signal, a light-receiving element for receiving the signal light and for generating a data signal in accordance with the signal light, a transmitting light wave guide for projecting transmission light that is the signal light from the light-emitting element to an optical fiber outside, and a received light wave guide for guiding received light that is signal light from the optical fiber outside, wherein: the transmitting light wave guide and the received light wave guide are mutually optically separated from each other, and at an area on each end face to which the transmitting light connected to the optical fiber is projected, the light axis of the transmission light is set so as to tilt with respect to the normal to the end face of the optical fiber.
In the above-mentioned arrangement, since the transmitting light wave guide and the received light wave guide are mutually optically separated, the above-mentioned arrangement eliminates the need for expensive optical elements conventionally used, such as polarizing beam splitters and wavelength filters, and carries out bidirectional optical communication simultaneously at low costs by using a simple system and a single optical fiber.
Moreover, in the above-mentioned arrangement, since the optical fiber transmits light in a multi-mode, the core diameter of the optical fiber can be made greater, for example, approximately 1 mm. Consequently, the above-mentioned arrangement makes it possible to easily couple the optical fiber and the bidirectional optical communication devices optically.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.